This invention relates to methods for pneumatically conveying slurry-like materials and more particularly to a method for conveying chicken hatchery waste products.
In a typical chicken hatchery operation, fertilized eggs are placed in hatchery trays which are then placed in an incubator for a predetermined amount of time until the eggs hatch. The newly hatched chicks are then removed from the tray for debeaking and innoculation prior to being sent to another location where they are fed and raised for subsequent sale to the consuming public.
After the newly hatched chicks had been removed from the trays, the trays contain a considerable amount of waste including egg shells, unhatched eggs as well as a few chicks which have been culled as being unsuitable for feeding and raising. Initially, the waste was manually dumped from trays into a dump truck, where it was exposed to the weather elements for as long as an entire six hour shift before being covered and transported to a land fill or other disposal area.
An improved system for disposing of hatchery waste was developed by Dickens, et al. (see U.S. Department of Agriculture, Agricultural Research Service Report entitled "A Vacuum System for Handling Chicken Hatchery Waste", October 1976, Paper No. ARS-S-152). The Dickens et al. system included a hopper into which the hatchery waste was dumped from the trays; a pump, or blower, to provide the force to transport the waste; and a receiver, to separate waste material from air and store the waste material until it was dumped into a transporting vehicle. The system also included duct work to connect the hopper, blower and receiver.
Hatchery waste material was a variable consistency which depends upon the percentage hatch, the number of culled chicks, as well as incidental quantities of floor waste, wash water and disinfectants which may find their way into the waste system. For example, if the hatch rate was 100% and there were no culled chicks and the incidental waste materials were prevented from entering the waste system, the hatchery waste composition would substantially comprise dry particulate matter composed of crushed egg shells. However, since these ideal conditions never exist, the waste usually has a slurry-like consistency which tended to cause problems in prior art waste handling systems like those disclosed in the Dickens et al. report. The more liquid the consistency, the more clogging problems one might encounter.
These clogging problems were recognized and partially solved (see, for example, the Dickens et al. report on page 6 where clogging in the duct work system was eliminated by reducing the angle of lift provided by the ducts from 90.degree. to 45.degree.). Another part of the system, in which clogging has been a major problem, is in the receiver in which the solid matter is separated and stored. Prior art waste handling systems incorporated several types of receivers, most of which were characterized by the fact that their waste material storage handling capability was limited. This limited storage handling capability was primarily due to the fact that the stored material had a tendency to bridge across the discharge aperture located at the bottom of the receiver and was thereby prevented from flowing out of the receiver into the transporting vehicle under the influence of gravity.
In large capacity receivers, a preferred configuration entails the use of a tapered portion at the bottom of the receiver which culminates in a reduced area discharge aperture. Having a reduced area discharge aperture is desirable since it is easier to provide an effective vacuum closure on a smaller aperture. An effective vacuum closure is necessary for the efficient operation of such a pneumatic conveying system, since leaks in the system would tend to reduce the conveying force provided by pressure differentials within the system. In addition, a smaller discharge aperture is desirable for mating with covered transporting vehicles. The tapered portion in large receivers aggravates the aforementioned bridging and concomitant clogging.
The use of a small receiver could also contribute to system clogging. In a typical pneumatic waste handling system, whenever it is desired to unload the receiver, the vacuum in the system is broken, the discharge aperture open and the waste material then disgorged from the receiver into a transporting vehicle under the influence of gravity. At those times when the vacuum is broken, any waste material that was in the process of being conveyed from the hopper to the receiver along any upwardly inclined conveying duct work, would then tend to flow backwards causing system clogging problems.
As can be determined from the previous discussion, the use of a small receiver in a pneumatic waste handling system is undesirable not only from the standpoint that the receiver would have to be unloaded relatively frequently during the course of the hatchery workers shift, but that system clogging could also be fostered by the frequent unloading operation. It is therefore desirable to use a large receiver if possible, preferably one which would store all wastes accumulated during the course of an entire shift.
As previously stated, in prior art systems the use of large receivers tends to create clogging problems in the receiver itself. One prior art solution to receiver clogging was to install water jets at the top of the receiver, which jets would spray water down on top of the stored material theoretically causing it to float down and out of the discharge aperture on the bottom of the receiver. Because of the material bridging effect, the water tended to remain on top of the clogged waste material.
Another solution to waste material clogging in the receiver was to use a large, straight walled receiver in which bridging would be minimized. A receiver having this configuration would necessitate the use of a large, difficult to seal, openable discharge aperture cover. The solution to the problem of an inefficient seal on the bottom of such a receiver was to use a knife gate valve in substantially the center of such a receiver. This knife gate valve divides the receiver into a top chamber and a bottom chamber, the bottom chamber terminating in a closure over the discharge aperture. This solution purported to enable the collection of waste materials in the top chamber during operation of the system, opening the knife gate valve and allowing the materials to fall into the bottom of the chamber without stopping the system, closing the knife gate valve in order to accumulate additional waste material in the top chamber, while being able to open the closure over the discharge aperture and allowing the materials to drop straight out of the bottom chamber. This solution required not only the use of an additional closure valve, the discharge aperture seal was still a problem while the knife gate valve was in the open position.